Clinical laboratory tests are routinely performed on the serum or plasma of whole blood. In a routine assay, red blood cells (RBC) are separated from plasma by centrifugation, or RBC's and various plasma proteins are separated from serum by clotting prior to centrifugation. Hemoglobin (Hb), light-scattering substances like lipid particles, and bile pigments bilirubin (BR) and biliverdin (BV) are typical blood components which will interfere with and affect spectrophotometric and other blood analytical measurements of blood analytes. Such components are referred to as interferents, and they can be measured by spectrophotometric methods. The presence of such interferents affects the ability to perform tests on the serum or plasma and as such can be said to compromise sample integrity.
Spectrophotometric measurements of blood analytes require proper calibration which can be monitored using quality control materials (QCM). QCM for blood analysis have been described in the prior art. For example U.S. Pat. No. 4,116,336 discloses the use of Amaranth or Ponceau 4 R as calibrators that mimic Hb, but these liquids must be enclosed in a flexible gas-tight container, at sub-atmospheric pressure. There is no teaching that this method is effective under atmospheric conditions. Furthermore, Amaranth and Ponceau 4 R were used separately to mimic Hb.
European Patent No. 0132399 suggests the use of one or more dyes (Acid Rhodamine B, Levafix Brilliant Yellow E-3G and Phloxine B; Phloxine Rhodamine and Atanyl Yellow 4NGL), which mimic the spectral response of whole blood and various levels of Hb in whole blood. There is no teaching of any substance or substances used to mimic an indicator of hemolysis or any analyte in serum or plasma.
WO 87/06343 discloses the use of a combination of Acid Red Dye #27 (CI 16185) and Acid Blue Dye #9 (CI 42090) and also a combination of Ponceau 3R Red Dye (CI 16155) and Acid Blue Dye #9 that simulate samples of whole blood having various levels of the fractions of Hb and of total Hb. There is no teaching of any substance or substances used to simulate an indicator of hemolysis or any analyte in serum or plasma.
Despite the fact that a number of QCM have been identified for various blood components, QCM for reagentless methods for measuring other components such as BR, BV, IL etc. are still needed. Furthermore no reliable method for selecting QCM has been described.
Warren (2001, Clinical Chemistry, Vol 47, No. 6, Supplement 2001) discloses the use of a serum pool for estimating the precision of several calibration algorithms. The use of the serum pool in monitoring the calibration algorithms is not taught.
WO-98/39634 and U.S. Pat. No. 6,268,910 B1 and U.S. Pat. No. 5,846,492 disclose methods for measuring Hb, IL, BR and BV in the presence of Hb, Hb-based blood substitute, IL, BR and BV, methods for measuring Hb-based blood substitute in the presence of Hb, IL, BR and BV, and methods for measuring Hb, IL, BR, BV and MB in the presence of Hb, IL, BR, BV and MB. However, they do not discuss QCM for monitoring calibration for any of the analytes.
It is an object of the present invention to overcome disadvantages of the prior art. This object is met by a combination of the features of the main claims. The subclaims disclose further advantageous embodiments of the invention.